With the improvement in diagnostic techniques as well as surgical techniques, the need for flexible materials which may be implanted in the body has grown rapidly. Thus, vascular prostheses are needed for replacement of diseased or traumatized vessels including aneurysms, patches are needed for covering relatively large openings in intestines or other organs such as may be caused by bullet wounds, patches are needed for reinforcing defective sections of intestines or esophagus and coverings are needed for implanted organs such as heart valves and pacemakers. A particularly pertinent example arises in the repair of detached retinas. At the present time, so-called eye-slings are fashioned from silicone plastic or fascia lata. In the procedure, the sling is sewn to the eyeball in such a fashion that it compresses the eyeball, the compression generally being such as to increase the internal pressure by some 30 mm of Hg. However, these materials may erode the eye or lead to infection since they are foreign bodies. Also, the use of facia lata involves a second operation since this material must be taken from the patient.
Considerable success has been achieved in the use of synthetic vascular grafts for replacement of defective arteries and veins. However, admirable as have been the results achieved with such synthetic materials, they have severe limitations. There is a substantial failure rate due to infection supervening and there may be biologic failure or degradation by fibrin layering, intimal or sub-intimal hyperplasia, and aneurysm formation. Perhaps the most important of the limitations is that grafts smaller than about 5 mm in inside diameter almost invariably become blocked by clots which form therein and clotting difficulties arise in certain bodily locations even with vascular grafts having inside diameters as great as 10 mm. Moreover, a delicate balance must be struck in the porosity of the synthetic graft since the wall thereof must be sufficiently porous to permit ingrowth and deposition of fibrin so that eventually the wall is covered with scar tissue both internally and externally and yet not be so porous that hemorrhage occurs. This makes it necessary to pre-clot the graft prior to use.
Such grafts are made, in general, either of polyester (Dacron) and Teflon. Fabrics woven or knitted of these polymers have also been useful as patches or reinforcements. However, the range of usefulness is restricted. As is obvious, the necessity for pre-clotting is a substantial disadvantage as is the fact that they occasionally cause inflammation. As aforenoted, a major disadvantage is the fact that they cannot reliably be used in the form of vessels having an inside diameter smaller than 5 mm. This precludes the possibility of replacement of coronary vessels as well as the minute vessels in fingers. Also, they do not give full reinforcement until they are completely overgrown with scar tissue.
Arterial homografts (human arteries) were used to restore continuity but limited supply, limited range of sizes and development of aneurysms and arterial sclerosis necessitated the search for better substitutes. In view of the difficulties encountered with the various types of artificially constructed grafts, these difficulties including: (1) infection which may lead to hemorrhage, sepsis and death; (2) thrombogenicity of the inner lining of the graft so that the graft is predisposed to clotting which may result in total occlusion of the graft and distal embolism of the clot; (3) the rigidity of fabric grafts which may result in twisting and kinking especially where a joint is crossed such twisting and kinking leading to graft occlusion, these must be considered as having serious deficiencies.
In the attempt to avoid artificial grafts, a variety of new techniques have been developed. These include "cleaning out" an artery such as by carbodissection, dilating arteries, development of bovine heterografts, and creating collagen tubes by inserting a mandrel within the recipient for later use of a graft.
It is known that homografts have been used for vascular grafting with considerable success. Commonly, the saphenous vein has been used in cases where the patient is the donor (an autograft) and where another human is a donor (allograft). These vessels require no treatment before implantation; however, they present problems of unavailability, disparity in size, nonuniform caliber, presence of valves and varicies, and the need for additional authorization in the case of allografts. The removal of the saphenous vein to be used for vascular grafting in the same patient involves keeping the patient on the table for a substantially longer time. Moreover, the operation is quite delicate and frequently is a failure. Finally, where rejection is a problem and the patient needs further grafting after the patient's own saphenous veins have been removed, repair by this method becomes impossible.
For these reasons as well as others which will appear it would be highly desirable to provide a new material for use as replacement and reinforcement for vessels and other organs of the body which would be free of the problems of clotting, thrombogenicity and antigenicity. Moreover, as will be disclosed herein, the new material proposed as a source for repair and replacement of vessels and other organs of the body can be prepared in a variety of forms which will give rise to new techniques of great usefulness.